Rapidly flashing or blinking objects are discouraged for use on Web sites, as they can trigger seizures in some users. Generally speaking, you should avoid objects which flicker or blink more than 3 times per second.
For more details on flicker guidelines, see the WCAG 2.3 Guideline: Seizures.
Items with gentle pulses or subtle dimming/lighting effects are effective while still meeting accessibility guidelines.
Some users, including those with certain types of epilepsy and migraines, may be susceptible to attacks or “episodes” when confronted with “loud” visual presentations. Particularly aggravating are:
- Rapidly blinking or animated objects, which can trigger an epileptic seizure in some users and headaches in others.
- Stripes, zig-zags and other types of geometric patterns, which can trigger migraines in some users.
- Strongly contrasting color schemes, which some users have reported cause headaches.